Data Interface for Point-to-Point Communications Between Devices

ABSTRACT

A data interface is provided for point-to-point communications between two devices, such as a read channel and a disk controller in an HDD system. An interface for communications from a transmitting device to a receiving device comprises a data bus configured to communicate m bits of data and a corresponding n bit data tag, wherein a given n bit data tag identifies a data type of a corresponding m bits of data on the data bus. An acknowledge signal from the receiving device optionally indicates that data on the data bus has been received and that the data on the data bus can be changed to a new value. A valid flag optionally indicates when a new predefined m-bit data value and corresponding n-bit tag value are on the data bus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 61/895,768, filed Oct. 25, 2013, entitled “Data Interface forPoint-To-Point Communications Between Devices,” incorporated byreference herein.

FIELD

The field relates generally to signal processing techniques, and moreparticularly to techniques for high speed point-to-point communicationsbetween devices.

BACKGROUND

Disk-based storage devices such as hard disk drives (HDDs) are commonlyused to provide non-volatile data storage in a wide variety of differenttypes of data processing systems. In such disk-based storage devices, aread channel typically sends Servo data to a disk controller over aS-wire interface (up to 2 bits per cycle) or by requesting a registeraddress over a standard Advanced Peripheral Bus (APB) or an AdvancedHigh Performance Bus (AHB). A need remains for improved data interfacesfor point-to-point communications between two devices, such as a readchannel and a disk controller in an HDD system.

SUMMARY

Generally, a data interface is provided for point-to-pointcommunications between two devices, such as a read channel and a diskcontroller in an HDD system. In one embodiment, an interface forcommunications from a transmitting device to a receiving devicecomprises a data bus configured to communicate m bits of data and acorresponding n bit data tag, wherein a given n bit data tag identifiesa data type of a corresponding m bits of data on the data bus.

In one exemplary synchronous embodiment, the n bit data tag and thecorresponding m bits of data change at substantially a same timerelative to a servo clock. In another asynchronous embodiment, the n bitdata tag and the corresponding m bits of data are stable for apredefined number of clock cycles after the n bit data tag changes.

The data bus optionally further communicates an acknowledge signal fromthe receiving device indicating that data on the data bus has beenreceived and that the data on the data bus can be changed to a newvalue. The data on the data bus is optionally maintained until theone-bit acknowledge signal has been set by the receiving device. Thedata bus optionally further communicates a valid flag indicating when anew predefined m-bit data value and corresponding n-bit tag value are onthe data bus.

In an exemplary read channel implementation, the transmitting devicecomprises read channel circuitry and the receiving device comprises adisk controller and wherein the data bus communicates one or more ofServo Address Mark (SAM) information, Gray Code information, burstdemodulation information, Repeatable Runout (RRO) information, SAM toSAM data; Servo Harmonic Sensor (SHS) information and Servo statusinformation.

Other embodiments of the invention include but are not limited tomethods, apparatus, systems, processing devices, integrated circuits andcomputer-readable storage media having computer program code embodiedtherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a disk-based storage device inaccordance with an illustrative embodiment of the invention;

FIG. 2 shows a plan view of a storage disk in the storage device of FIG.1;

FIG. 3 is a block diagram of a portion of the storage device of FIG. 1including an exemplary system-on-chip comprising a disk controller andread channel circuitry;

FIGS. 4A and 4B are flow charts illustrating an exemplary interfaceprotocol implemented by the read channel circuitry and disk controller,respectively, of FIG. 3 to transfer data over the interface inaccordance with aspects of the present invention;

FIG. 5 provides a sample table indicating an exemplary assignment ofeach exemplary n-bit tag value to a corresponding data format to furtherspecify assignment within the m-bit data value;

FIG. 6A is a sample table illustrating an exemplary bit assignment forexemplary SAM data;

FIG. 6B is a sample table illustrating an exemplary bit assignment forexemplary RRO data;

FIGS. 7A and 7B provide exemplary timing diagrams to illustrate theoperation of the exemplary interface of FIG. 3;

FIG. 8 illustrates interconnection of the storage device of FIG. 1 witha host processing device in a data processing system; and

FIG. 9 shows a virtual storage system incorporating a plurality ofdisk-based storage devices of the type shown in FIG. 1.

DETAILED DESCRIPTION

Embodiments of the invention will be illustrated herein in conjunctionwith exemplary disk-based storage devices write drivers and associatedcircuitry. While the present invention is illustrated in the context ofan exemplary interface for exemplary communications between a readchannel and a disk controller in an HDD system, it should be understoodthat these and other embodiments of the invention are more generallyapplicable to any environment in which improved point-to-pointcommunications between devices are desired. Additional embodiments maybe implemented using components other than those specifically shown anddescribed in conjunction with the illustrative embodiments.

FIG. 1 shows a disk-based storage device 100 in accordance with anillustrative embodiment of the invention. The storage device 100 in thisembodiment more specifically comprises an HDD that includes a storagedisk 110. The storage disk 110 has a storage surface coated with one ormore magnetic materials that are capable of storing data bits in theform of respective groups of media grains oriented in a commonmagnetization direction (e.g., up or down). The storage disk 110 isconnected to a spindle 120. The spindle 120 is driven by a spindlemotor, not explicitly shown in the figure, in order to spin the storagedisk 110 at high speed.

Data is read from and written to the storage disk 110 via a read/writehead 130 that is mounted on a positioning arm 140. It is to beappreciated that the head 130 is shown only generally in FIG. 1. Theposition of the read/write head 130 over the magnetic surface of thestorage disk 110 is controlled by an electromagnetic actuator 150. Theelectromagnetic actuator 150 and its associated driver circuitry in thepresent embodiment may be viewed as comprising a portion of what is moregenerally referred to herein as “control circuitry” of the storagedevice 100. Such control circuitry in this embodiment is assumed tofurther include additional electronics components arranged on anopposite side of the assembly and therefore not visible in theperspective view of FIG. 1.

The term “control circuitry” as used herein is therefore intended to bebroadly construed so as to encompass, by way of example and withoutlimitation, drive electronics, signal processing electronics, andassociated processing and memory circuitry, and may encompass additionalor alternative elements utilized to control positioning of a read/writehead relative to a storage surface of a storage disk in a storagedevice. A connector 160 is used to connect the storage device 100 to ahost computer or other related processing device.

It is to be appreciated that, although FIG. 1 shows an embodiment of theinvention with only one instance of each of the single storage disk 110,read/write head 130, and positioning arm 140, this is by way ofillustrative example only, and alternative embodiments of the inventionmay comprise multiple instances of one or more of these or other drivecomponents. For example, one such alternative embodiment may comprisemultiple storage disks attached to the same spindle so all such disksrotate at the same speed, and multiple read/write heads and associatedpositioning arms coupled to one or more actuators. Also, both sides ofstorage disk 110 and any other storage disks in a particular embodimentmay be used to store data and accordingly may be subject to read andwrite operations, through appropriate configuration of one or moreread/write heads.

A given read/write head as that term is broadly used herein may beimplemented in the form of a combination of separate read and writeheads. More particularly, the term “read/write” as used herein isintended to be construed broadly as read and/or write, such that aread/write head may comprise a read head only, a write head only, asingle head used for both reading and writing, or a combination ofseparate read and write heads. A given read/write head such asread/write head 130 may therefore include both a read head and a writehead. Such heads may comprise, for example, write heads with wrap-aroundor side-shielded main poles, or any other types of heads suitable forrecording and/or reading data on a storage disk. Read/write head 130when performing write operations may be referred to herein as simply awrite head.

Also, the storage device 100 as illustrated in FIG. 1 may include otherelements in addition to or in place of those specifically shown,including one or more elements of a type commonly found in aconventional implementation of such a storage device. These and otherconventional elements, being well understood by those skilled in theart, are not described in detail herein. It should also be understoodthat the particular arrangement of elements shown in FIG. 1 is presentedby way of illustrative example only. Those skilled in the art willrecognize that a wide variety of other storage device configurations maybe used in implementing embodiments of the invention.

FIG. 2 shows the storage surface of the storage disk 110 in greaterdetail. As illustrated, the storage surface of storage disk 110comprises a plurality of concentric tracks 210. Each track is subdividedinto a plurality of sectors 220 which are capable of storing a block ofdata for subsequent retrieval. The tracks located toward the outsideedge of the storage disk have a larger circumference when compared tothose located toward the center of the storage disk. The tracks aregrouped into several annular zones 230, where the tracks within a givenone of the zones have the same number of sectors. Those tracks in theouter zones have more sectors than those located in the inner zones. Inthis example, it is assumed that the storage disk 110 comprises M+1zones, including an outermost zone 230-0 and an innermost zone 230-M.

The outer zones of the storage disk 110 provide a higher data transferrate than the inner zones. This is in part due to the fact that thestorage disk in the present embodiment, once accelerated to rotate atoperational speed, spins at a constant angular or radial speedregardless of the positioning of the read/write head, but the tracks ofthe inner zones have smaller circumference than those of the outerzones. Thus, when the read/write head is positioned over one of thetracks of an outer zone, it covers a greater linear distance along thedisk surface for a given 360° turn of the storage disk than when it ispositioned over one of the tracks of an inner zone. Such an arrangementis referred to as having constant angular velocity (CAV), since each360° turn of the storage disk takes the same amount of time, although itshould be understood that CAV operation is not a requirement ofembodiments of the invention.

Areal and linear bit densities are generally constant across the entirestorage surface of the storage disk 110, which results in higher datatransfer rates at the outer zones. Accordingly, the outermost annularzone 230-0 of the storage disk has a higher average data transfer ratethan the innermost annular zone 230-M of the storage disk. The averagedata transfer rates may differ between the innermost and outermostannular zones in a given embodiment by more than a factor of two. As oneexample embodiment, provided by way of illustration only, the outermostannular zone may have a data transfer rate of approximately 2.3 Gb/s,while the innermost annular zone has a data transfer rate ofapproximately 1.0 Gb/s. In such an implementation, the HDD may moreparticularly have a total storage capacity of 500 Gigabytes (GB) and aspindle speed of 7200 revolutions per minute (RPM), with the datatransfer rates ranging, as noted above, from about 2.3 Gb/s for theoutermost zone to about 1.0 Gb/s for the innermost zone.

The storage disk 110 may be assumed to include a timing pattern formedon its storage surface. Such a timing pattern may comprise one or moresets of servo address marks (SAMs) or other types of servo marks formedin particular sectors in a conventional manner.

The particular data transfer rates and other features referred to in theembodiment described above are presented for purposes of illustrationonly, and should not be construed as limiting in any way. A wide varietyof other data transfer rates and storage disk configurations may be usedin other embodiments.

FIG. 3 shows a portion of the storage device 100 of FIG. 1 in greaterdetail. In this view, the storage device 100 comprises a processor 300,a memory 302 and a system-on-a-chip (SOC) 304, which communicate over abus 306. The storage device further comprises driver circuitry 305providing an interface between the SOC 304 and the read/write head 130.The driver circuitry 305 may comprise, for example, a preamplifier andother associated interface circuitry. The memory 302 is an externalmemory relative to the SOC 304 and other components of the storagedevice 100, but is nonetheless internal to that storage device. Theread/write head 130 and storage disk 110 are collectively denoted inFIG. 3 as comprising a head disk assembly (HDA) 308.

The SOC 304 in the present embodiment includes read channel circuitry310 and a disk controller 312, and directs the operation of theread/write head 130 in reading data from and writing data to the storagedisk 110. The read channel circuitry 310 and the disk controller 312communicate with one another over one or more interface connections 314that may be viewed as representing a portion of the bus 306.

As discussed further below in conjunction with FIGS. 4 through 9, theexemplary interface connection 314 provides improved point-to-pointcommunications between the exemplary read channel circuitry 310 and theexemplary disk controller 312 in accordance with aspects of the presentinvention.

The bus 306 may comprise, for example, one or more interconnect fabrics.Such fabrics may be implemented in the present embodiment as AdvancedeXtensible Interface (AXI) fabrics, described in greater detail in, forexample, the Advanced Microcontroller Bus Architecture (AMBA) AXI v2.0Specification, which is incorporated by reference herein. The bus mayalso be used to support communications between other system components,such as between the SOC 304 and the driver circuitry 305. It should beunderstood that AXI interconnects are not required, and that a widevariety of other types of bus configurations may be used in embodimentsof the invention.

The processor 300, memory 302, SOC 304 and driver circuitry 305 may beviewed as collectively comprising one possible example of “controlcircuitry” as that term is utilized herein. Numerous alternativearrangements of control circuitry may be used in other embodiments, andsuch arrangements may include only a subset of the components 300, 302,304 and 305, or portions of one or more of these components. Forexample, the SOC 304 itself may be viewed as an example of “controlcircuitry.” As noted above, the control circuitry of the storage device100 in the embodiment as shown in FIG. 3 is generally configured toprocess data received from and supplied to the read/write head 130 andto control positioning of the read/write head 130 relative to thestorage disk 110.

It should be noted that certain operations of the SOC 304 in the storagedevice 100 of FIG. 3 may be directed by processor 300, which executescode stored in external memory 302. For example, the processor 300 maybe configured to execute code stored in the memory 302 for performing atleast a portion of an ITI-based head position control process carriedout by the SOC 304. Thus, at least a portion of the ITI detection andhead position control functionality of the storage device 100 may beimplemented at least in part in the form of software code.

The external memory 302 may comprise electronic memory such as randomaccess memory (RAM) or read-only memory (ROM), in any combination. Inthe present embodiment, it is assumed without limitation that theexternal memory 302 is implemented at least in part as a double datarate (DDR) synchronous dynamic RAM (SDRAM). The memory 302 is an exampleof what is more generally referred to herein as a “computer-readablestorage medium.” Such a medium may also be writable.

Although the SOC 304 in the present embodiment is assumed to beimplemented on a single integrated circuit, that integrated circuit mayfurther comprise portions of the processor 300, memory 302, drivercircuitry 305 and bus 306. Alternatively, portions of the processor 300,memory 302, driver circuitry 305 and bus 306 may be implemented at leastin part in the form of one or more additional integrated circuits, suchas otherwise conventional integrated circuits designed for use in an HDDand suitably modified to provide ITI-base head position controlfunctionality as disclosed herein.

An example of an SOC integrated circuit that may be modified toincorporate an embodiment of the present invention is disclosed in U.S.Pat. No. 7,872,825, entitled “Data Storage Drive with Reduced PowerConsumption,” which is commonly assigned herewith and incorporated byreference herein.

Other types of integrated circuits that may be used to implementprocessor, memory or other storage device components of a givenembodiment include, for example, a microprocessor, digital signalprocessor (DSP), application-specific integrated circuit (ASIC),field-programmable gate array (FPGA) or other integrated circuit device.

In an embodiment comprising an integrated circuit implementation,multiple integrated circuit dies may be formed in a repeated pattern ona surface of a wafer. Each such die may include a device as describedherein, and may include other structures or circuits. The dies are cutor diced from the wafer, then packaged as integrated circuits. Oneskilled in the art would know how to dice wafers and package dies toproduce packaged integrated circuits. Integrated circuits somanufactured are considered embodiments of the invention.

Although shown as part of the storage device 100 in the presentembodiment, one or both of the processor 300 and memory 302 may beimplemented at least in part within an associated processing device,such as a host computer or server in which the storage device isinstalled. Accordingly, elements 300 and 302 in the FIG. 3 embodimentmay be viewed as being separate from the storage device 100, or asrepresenting composite elements each including separate processing ormemory circuitry components from both the storage device and itsassociated processing device. As noted above, at least portions of theprocessor 300 and memory 302 may be viewed as comprising “controlcircuitry” as that term is broadly defined herein.

Servo Fast Data Interface

As indicated above, the exemplary interface 314 provides improvedpoint-to-point communications from the exemplary read channel circuitry310 to the exemplary disk controller 312 in accordance with aspects ofthe present invention. The exemplary interface 314 is also referred toherein as a Servo Fast Data Interface (srv_fdi). The exemplary interface314 is implemented as a 32-bit data bus (srv_fdi[31:0]) and a separate4-bit (for example) tag bus (srv_fdi_tag[3:0]) indicating the type ofdata currently on the exemplary interface 314, as discussed furtherbelow in conjunction with FIG. 5. The 4-bit tag bus (srv_fdi_tag[3:0])can be expanded to additional bits if more data fields are required. Inaddition, an optional one-bit valid flag (srv_fdi_valid) indicates whena new non-zero value is on the 32-bit bus (srv_fdi[31:0]) and the 4-bittag bus (srv_fdi_tag[3:0]). While the exemplary embodiment is discussedherein using a 32-bit data bus (srv_fdi[31:0]) and a 4-bit tag bus(srv_fdi_tag[3:0]), in alternate embodiments, the number of bits on eachbus can be varied and the two buses can be combined to form a singlebus, as would be apparent to a person of ordinary skill in the art.

An optional one-bit acknowledge signal (srv_fdi_ack) from the diskcontroller 312 indicates that the current data has been received by thedisk controller 312 and that the exemplary interface 314 can be changedby the exemplary interface 314 to the next value, to provide a handshakemechanism. In a handshake mode, the data does not change until after theone-bit acknowledge signal (srv_fdi_ack) is set to 1. In an exemplarynon-handshake mode, the one-bit acknowledge signal (srv_fdi_ack) ispermanently set to a value of 1. In a non-handshake mode, (wheresrv_fdi_ack is tied to 1) the value on the 32-bit data bus(srv_fdi[31:0]) is held for, for example, 3 cycles.

In this manner, each 32-bit value placed on the exemplary interface 314is accompanied by a 4-bit tag on 4-bit tag bus (srv_fdi_tag[3:0]) thatindicates the type of data on the 32-bit exemplary interface 314srv_fdi[31:0]. The value on 4-bit tag bus (srv_fdi_tag[3:0]) changes atthe same time as the data on 32-bit bus (srv_fdi[31:0]) and can be helduntil the next cycle at which srv_fdi_ack is set to binary one.

As discussed hereinafter, the exemplary interface 314 allows the diskcontroller 312 to receive data, such as Servo event status information,from the exemplary read channel circuitry 310. In the exemplaryembodiment discussed herein, the exemplary interface 314 allows the diskcontroller 312 to receive the following exemplary data from theexemplary read channel circuitry 310:

Servo Address Mark (SAM) Found including SAM Status;

Gray Code;

Burst Demodulation Results;

Repeatable Runout (RRO) Status and Data;

SAM to SAM Distance Data;

Servo Harmonic Sensor Results; and

Servo Status.

FIG. 4A is a flow chart illustrating an exemplary interface protocol 400implemented by the exemplary read channel circuitry 310 to send dataover the interface 314 to the disk controller 312 in accordance withaspects of the present invention. As shown in FIG. 4A, once theexemplary read channel circuitry 310 has data to send (step 410), theexemplary read channel circuitry 310 will set the optional one-bit validflag (srv_fdi_valid) to a value of binary one, and then place the dataon the 32-bit data bus (srv_fdi[31:0]) and place the appropriate tag forthe data on the 4-bit tag bus (srv_fdi_tag[3:0]) during step 420.

FIG. 4B is a flow chart illustrating an exemplary interface protocol 400implemented by the disk controller 312 to obtain data over the interface314 from the read channel circuit 310 in accordance with aspects of thepresent invention. As shown in FIG. 4B, the disk controller 312 willmonitor the 4-bit tag bus (srv_fdi_tag[3:0]) on the interface 314 duringstep 450 for a non-zero value. When the disk controller 312 sees anon-zero value on the exemplary interface 314, the disk controller 312will capture both srv_fdi and srv_fdi_tag from the interface 314 duringstep 460 for processing, and optionally set the one-bit acknowledgesignal (srv_fdi_ack) once the data has been captured. It is again notedthat the 4-bit tag bus (srv_fdi_tag[3:0]) indicates the type of data onthe exemplary 32-bit bus (srv_fdi[31:0]).

As discussed further below in conjunction with FIG. 7, thesrv_fdi[31:0], srv_fdi_valid and srv_fdi_tag[3:0] are synchronous to therising edge of a one-bit servo clock (srv_clk), used in an optionalsynchronous mode. In a synchronous mode, the 4-bit tag bus(srv_fdi_tag[3:0]) and the 32-bit data bus (srv_fdi[31:0]) change at thesame time relative to the servo clock (srv_clk). In an asynchronousmode, the data bus must be stable one cycle before and one cycle afterthe 4-bit tag bus (srv_fdi_tag[3:0]) tag changes.

In a handshake mode (not shown in FIGS. 4A and 4B), after capturingsrv_fdi and srv_fdi_tag from the exemplary interface 314 during step430, the disk controller 312 will set the exemplary one-bit acknowledgesignal (srv_fdi_ack) to a value of binary one at which time the O-bittag bus (srv_fdi_tag[3:0]) shall be set to 0 until the next data fieldis available.

FIG. 5 provides a sample table 500 indicating an exemplary assignment ofeach exemplary 4 bit tag value to a corresponding data format to furtherspecify assignment within 32 bits. For example, when the 4-bit tag bus(srv_fdi_tag[3:0]) is set to 0x1, additional information will beprovided on the 32-bit bus (srv_fdi[31:0]) about the SAM. As discussedfurther below in conjunction with FIG. 6A, this additional informationcan include which SAM pattern was found, the SAM Quality and Timeout.

The Gray Code can be transferred on the 32-bit bus (srv_fdi[31:0]) afterthe SAM is found. As shown in FIG. 5, the first value transferred afterthe SAM is found is GRAYL[31:0] with a O-bit tag of 0x2 and the secondvalue transferred after the SAM is found is GRAYH[63:32] with a 4-bittag of 0x3, when the number of gray bits (NGRAY) exceeds 32. Thus, theGray Code can be transferred in one transfer if NGRAY is less than orequal to 32, and in two transfers if NGRAY is greater than 32.

Up to 4 data bursts can be present in a Servo Event and burstdemodulation results are transferred on the exemplary interface 314. Inan exemplary embodiment of the present invention, burst data iscontrolled based on a number of bursts (NBURSTS) and the selection ofwhich results to place on the exemplary interface 314 is controlled by a3-bit demodulation value (DEMOD_MD). Each burst is transferredseparately on the exemplary interface 314.

Additional conventions can be established to transfer additional data onthe exemplary interface 314, as would be apparent to a person ofordinary skill in the art. For example, RRO Data can be controlled by anRRO length valuate (RRO_LEN) and RRO mode (RRO_MD). Thus, the RRO Datacan be transferred in one transfer if RRO_LEN is less than or equal to32, and in two transfers if RRO_LEN is greater than 32.

The 32-bit data bus (srv_fdi[31:0]) bus can contain full 32-bit valuesor can be broken up into different, shorter values. For example, FIG. 6Ais a sample table 600 illustrating an exemplary bit assignment forexemplary SAM data. Likewise, FIG. 6B is a sample table 650 illustratingan exemplary bit assignment for exemplary RRO data.

FIGS. 7A and 7B provide exemplary timing diagrams 700, 750 to illustratethe operation of the exemplary interface 314. In the example of FIG. 7A,the exemplary timing diagram 700 illustrates the various signals presenton the exemplary interface 314 to transmit SAM information, two GrayCodes (where NGRAY>32) and one burst. As shown in FIG. 7A, the exemplaryservo clock (srv_clk) runs at a 4T rate without gaps.

The one-bit valid flag (srv_fdi_valid) indicates when a new non-zerovalue is on the 32-bit bus (srv_fdi[31:0]) and the 4-bit tag bus(srv_fdi_tag[3:0]). The disk controller 312 will detect the non-zerovalues and capture the corresponding values on the 32-bit bus(srv_fdi[31:0]) and the O-bit tag bus (srv_fdi_tag[3:0]). The capturedvalue on the 32-bit bus (srv_fdi[31:0]) is interpreted based on the datatype specified by the corresponding captured value on the 4-bit tag bus(srv_fdi_tag[3:0]).

As shown in FIG. 7A, both the 32-bit data bus (srv_fdi[31:0]) and the4-bit tag bus (srv_fdi_tag[3:0]) are set to zero when there is no datato transmit. When the exemplary read channel circuitry 310 has data tosend to the disk controller 312, the exemplary read channel circuitry310 sets the one-bit valid flag (srv_fdi_valid) and places the data onthe 32-bit data bus (srv_fdi[31:0]) with the corresponding data type ofthe data on the 4-bit tag bus (srv_fdi_tag[3:0]). For example, whentransmitting the SAM data on the 32-bit data bus (srv_fdi[31:0]), the4-bit tag bus (srv_fdi_tag[3:0]) is set to 0x1. In addition, whentransmitting a Gray Code that exceeds 32 bits on the 32-bit data bus(srv_fdi[31:0]), the first Gray value (GRAYL[31:0]) is transferred witha 4-bit tag of 0x2 and the second value (GRAYH[63:32]) is transferredwith a 4-bit tag of 0x3. A single data burst is then transferred on theexemplary 32-bit data bus (srv_fdi[31:0]) with a 4-bit tag of 0x4.

FIG. 7A also illustrates that the 32-bit data bus (srv_fdi[31:0]), 4-bittag bus (srv_fdi_tag[3:0]) and the one-bit valid flag (srv_fdi_valid)are synchronous in the exemplary embodiment to the rising edge of theservo clock (srv_clk). In addition, the values on the exemplary buseswill not change until two cycles after a rising edge of the one-bitacknowledge signal (srv_fdi_ack). The position of the rising edge of theexemplary one-bit acknowledge signal (srv_fdi_ack) may be delayed fromthe illustrative position shown in FIG. 7A.

In the example of FIG. 7B, the exemplary timing diagram 750 illustratesthe various signals present on the exemplary interface 314 to transmitSAM data, a Gray Code (where NGRAY<32), two data bursts, RRO data,SAM2SAM data, Servo Harmonic Sensor (SHS) data and Status information.When the exemplary read channel circuitry 310 has data to send to thedisk controller 312, the exemplary read channel circuitry 310 sets theone-bit valid flag (srv_fdi_valid) and places the data on the 32-bitdata bus (srv_fdi[31:0]) with the corresponding data type of the data onthe 4-bit tag bus (srv_fdi_tag[3:0]). For example, when transmitting theSAM data on the 32-bit data bus (srv_fdi[31:0]), the 4-bit tag bus(srv_fdi_tag[3:0]) is set to 0x1. In addition, when transmitting a GrayCode that does not exceed 32 bits on the 32-bit data bus(srv_fdi[31:0]), the Gray value (GRAYL[31:0]) is transferred with a4-bit tag of 0x2. A first data burst is then transferred on theexemplary 32-bit data bus (srv_fdi[31:0]) with a 4-bit tag of 0x4 and asecond data burst is then transferred on the exemplary 32-bit data bus(srv_fdi[31:0]) with a 4-bit tag of 0x5.

RRO status is then transferred on the exemplary 32-bit data bus(srv_fdi[31:0]) with a O-bit tag of 0x8 and RRO data (up to 32 bits) istransferred on the exemplary 32-bit data bus (srv_fdi[31:0]) with a4-bit tag of 0x9. Status data is then transferred on the exemplary32-bit data bus (srv_fdi[31:0]) with a 4-bit tag of 0xB, followed bySAM-to-SAM data with a 4-bit tag of 0xC. SHS_MAG1 and SHS_MAG3 data aretransferred with 4-bit tags of 0xD and 0xE, respectively. As shown inFIG. 7B, RRO Status/RRO Data and SHS_MAG1/SHS_MAG3 data can be sentwithout a gap between values.

As indicated above, the exemplary interface 314 is a synchronous,two-way interface that optionally includes an acknowledgement indicatingthat the data on the 32-bit data bus (srv_fdi[31:0]) has been capturedby the disk controller 312 and can be changed by the exemplary readchannel circuitry 310 to the next value. Thus, when the disk controller312 captures the srv_fdi[31:0] data, the disk controller 312 setssrv_fdi_ack to a value of binary one. The one-bit acknowledge signal(srv_fdi_ack) can be launched on the rising edge of the servo clock(srv_clk) received by the controller to minimize the turn-around time ofthe acknowledgement. Once the exemplary read channel circuitry 310(Servo) receives the one-bit acknowledge signal (srv_fdi_ack), the dataon the 32-bit data bus (srv_fdi[31:0]) and the 4-bit tag bus(srv_fdi_tag[3:0]) may be changed. If no data is available, theexemplary read channel circuitry 310 sets the 32-bit data bus(srv_fdi[31:0]) and 4-bit tag bus (srv_fdi_tag[3:0]) to 0 until the nextvalue to be transferred is available.

Only a single acknowledgement is processed for each 4-bit tag(srv_fdi_tag[3:0]) value. If the one-bit acknowledge signal(srv_fdi_ack) is set to one for multiple cycles prior to the 4-bit tagbus (srv_fdi_tag[3:0]) changing value, only the first occurrence of theone-bit acknowledge signal (srv_fdi_ack) set to one is recognized as anacknowledgement.

If a servo event ends without a required acknowledgement being received,the exemplary 32-bit data bus (srv_fdi[31:0]) and 4-bit tag bus(srv_fdi_tag[3:0]) hold the last value transferred until anacknowledgement (ack) is received. After the acknowledgement isreceived, the next valid tag shall be loaded on the 4-bit tag bus(srv_fdi_tag[3:0]). If no acknowledgement is received, the exemplary32-bit data bus (srv_fdi[31:0]) and 4-bit tag bus (srv_fdi_tag[3:0])continue holding the last value until the start of the next servo event.

In a “no handshake” mode (where srv_fdi_ack is held at 1), if a servoevent ends and srv_fdi_ack continues being held at a value of one, theexemplary interface 314 continues transferring the data on srv_fdi[31:0]along with the corresponding tag on srv_fdi_tag[31:0]. If srv_fdi_ackgoes to 0, then the 32-bit data bus (srv_fdi[31:0]) and 4-bit tag bus(srv_fdi_tag[3:0]) continue holding the last value until the start ofthe next servo event. In addition, the servo clock (srv_clk) continuestoggling at the programmed rate until the start of the next servo eventor until Servo Clock Select (SRVCKON) is changed. Generally, whenSRVCKON is set to 0, the servo clock (srv_clk) toggles only during anactive servo event until the last values on srv_fdi and srv_fdi_tag areacknowledged. When SRVCKON is set to 1, srv_clk toggles at all times.The changing of SRVCKON only stops the servo clock (srv_clk), the 32-bitdata bus (srv_fdi[31:0]) and 4-bit tag bus (srv_fdi_tag[3:0]) do notchange values.

FIG. 8 illustrates a processing system 800 comprising the disk-basedstorage device 100 coupled to a host processing device 802, which may bea computer, server, communication device, etc. Although shown as aseparate element in this figure, the storage device 100 may beincorporated into the host processing device. Instructions such as readcommands and write commands directed to the storage device 100 mayoriginate from the processing device 802, which may comprise processorand memory elements similar to those previously described in conjunctionwith FIG. 3.

Multiple storage devices 100-1 through 100-N possibly of variousdifferent types may be incorporated into a virtual storage system 900 asillustrated in FIG. 9. The virtual storage system 900, also referred toas a storage virtualization system, illustratively comprises a virtualstorage controller 902 coupled to a RAID system 904, where RAID denotesRedundant Array of Independent storage Devices. The RAID system 904 morespecifically comprises N distinct storage devices denoted 100-1, 100-2,. . . 100-N, one or more of which may be HDDs and one or more of whichmay be solid state drives. Furthermore, one or more of the HDDs of theRAID system 904 are assumed to include the exemplary interface 314 asdisclosed herein. These and other virtual storage systems comprisingHDDs or other storage devices of the type disclosed herein areconsidered embodiments of the invention. The host processing device 802in FIG. 8 may also be an element of a virtual storage system such assystem 900, and may incorporate the virtual storage controller 902.

While the exemplary interface 314 provides improved point-to-pointcommunications from the exemplary read channel circuitry 310 to theexemplary disk controller 312 in accordance with aspects of the presentinvention, it is noted that the exemplary interface 314 can providepoint-to-point communications from the exemplary disk controller 312 tothe exemplary read channel circuitry 310, as well as bidirectionalcommunications between the exemplary read channel circuitry 310 and theexemplary disk controller 312.

Again, it should be emphasized that the above-described embodiments ofthe invention are intended to be illustrative only. For example, otherembodiments can use different types and arrangements of storage media,write heads, control circuitry, preamplifiers, write drivers and otherstorage device elements for implementing the described data interface314 for point-to-point communications between devices, such as theexemplary read channel circuitry 310 and disk controller 312. These andnumerous other alternative embodiments within the scope of the followingclaims will be apparent to those skilled in the art.

What is claimed is:
 1. An interface for communications from atransmitting device to a receiving device, comprising: a data busconfigured to communicate m bits of data and a corresponding n bit datatag, wherein a given n bit data tag identifies a data type of acorresponding m bits of data on said data bus.
 2. The interface of claim1 wherein the n bit data tag and said corresponding m bits of datachange at substantially a same time relative to a servo clock in asynchronous mode.
 3. The interface of claim 1 wherein the n bit data tagand said corresponding m bits of data are stable for a predefined numberof clock cycles after said n bit data tag changes in an asynchronousmode.
 4. The interface of claim 1 wherein the data bus furthercommunicates an acknowledge signal from the receiving device indicatingthat data on the data bus has been received and that the data on thedata bus can be changed to a new value.
 5. The interface of claim 4wherein the data on the data bus is maintained until the one-bitacknowledge signal has been set by the receiving device.
 6. Theinterface of claim 1 wherein the data bus further communicates a validflag indicating when a new predefined m-bit data value and correspondingn-bit tag value are on the data bus.
 7. The interface of claim 1 whereina given m bits of data on said data bus is interpreted based on saidcorresponding n bit data tag.
 8. The interface of claim 1 wherein thetransmitting device comprises read channel circuitry and the receivingdevice comprises a disk controller and wherein the data bus communicatesone or more of Servo Address Mark (SAM) information, Gray Codeinformation, burst demodulation information, Repeatable Runout (RRO)information, SAM to SAM data; Servo Harmonic Sensor (SHS) informationand Servo status information.
 9. The interface of claim 1 wherein thecommunications are bidirectional between said transmitting device andsaid receiving device.
 10. The interface of claim 1 wherein the data buscomprises a first bus configured to communicate said m bits of data anda second bus configured to communicate said corresponding n bit datatag.
 11. The interface of claim 1 wherein the interface is fabricated inat least one integrated circuit.
 12. The interface of claim 11 whereinthe integrated circuit further comprises: at least one disk controller;and at least one read channel circuit.
 13. A storage device comprisingthe interface of claim
 1. 14. A virtual storage system comprising thestorage device of claim
 13. 15. A method for communicating from atransmitting device to a receiving device comprising the steps of:writing m bits of data to a data bus connecting said transmitting deviceand said receiving device; and writing an n bit data tag to said databus corresponding to said m bits of data, wherein a given n bit data tagidentifies a data type of a corresponding m bits of data on said databus.
 16. The method of claim 15 wherein the n bit data tag and saidcorresponding m bits of data change at substantially a same timerelative to a servo clock in a synchronous mode.
 17. The method of claim15 wherein the n bit data tag and said corresponding m bits of data arestable for a predefined number of clock cycles after said n bit data tagchanges in an asynchronous mode.
 18. The method of claim 15 furthercomprising the step of communicating an acknowledge signal from thereceiving device indicating that data on the data bus has been receivedand that the data on the data bus can be changed to a new value.
 19. Themethod of claim 18 further comprising the step of maintaining data onthe data bus until the one-bit acknowledge signal has been set by thereceiving device.
 20. The method of claim 15 further comprising the stepof communicating a valid flag indicating when a new predefined m-bitdata value and corresponding n-bit tag value are on the data bus. 21.The method of claim 15 wherein the transmitting device comprises readchannel circuitry and the receiving device comprises a disk controllerand wherein the data bus communicates one or more of Servo Address Mark(SAM) information, Gray Code information, burst demodulationinformation, Repeatable Runout (RRO) information, SAM to SAM data; ServoHarmonic Sensor (SHS) information and Servo status information.
 22. Themethod of claim 15 wherein the data bus comprises a first bus configuredto communicate said m bits of data and a second bus configured tocommunicate said corresponding n bit data tag.
 23. A processing systemcomprising: a processing device; and an interface configured tocommunicate with a receiving device, comprising: a data bus forcommunicating m bits of data and a corresponding n bit data tag, whereina given n bit data tag identifies a data type of a corresponding m bitsof data on said data bus.